Mass production
-
Different species and strains of Trichogramma typically prefer different host eggs and crop habitats and have different searching abilities and tolerance to weather conditions.
-
Efficacy is improved by selecting the most effective and adapted species or strain for the specific crop / pest situation.
-
In the laboratory the parasitoids are multiplied on Corcyra eggs. The eggs laid by the Corcyra moths are collected and sieved to remove the moth scales etc.
-
The pure eggs thus obtained are exposed to ultra-violet light in UV chamber to kill the host embryo but at the same time permit parasitization.
-
The quantity of the sterilized eggs is assessed in a measuring cylinder volumetrically. The eggs in volume of six cc are then sprinkled uniformly over a 144 gsm (chart paper) card of 30 x 18 cm size (Fig.1).
|
|
| |
Trichogramma parasitized on egg |
- The card is divided into two halves of 30 x 9 cm (LxB). Lengthwise it is subdivided into 15 grids (G1 to G15) of size 2cm. The dimension of each grid is 7x2 cm. Each grid can accommodate 0.2 cc of the eggs.
- Label information on the manufacturer, species of the parasitoid, date of parasitization and expected date of emergence are given in the left over spaces of size 30 x 1 cm on the top and bottom of each half of the card.
Fig.1. Trichogramma Card
|
1 cm |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
| G1 7x2 cm |
G2 |
G3 |
G4 |
G5 |
G6 |
G7 |
G8 |
G9 |
G10 |
G11 |
G12 |
G13 |
G14 |
G15 |
| 1 cm |
Trichogramma chilonis |
Date of parasitisation : |
Date of emergence expected : |
| 1 cm |
Trichogramma chilonis |
Date of parasitisation : |
Date of emergence expected : |
| G16 |
G17 |
G18 |
G19 |
G20 |
G21 |
G22 |
G23 |
G24 |
G25 |
G26 |
G27 |
G28 |
G29 |
G30 |
| 1 cm |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
TNAU |
- A coat of 10% gum arabic is applied on the grids (G1-30) and the eggs are sprinkled uniformly in a single layer with the aid of a tea strainer.
- The excess eggs pasted are removed by gently passing a shoe brush over the card after sufficient air drying under fan.
- The egg cards are placed into polythene bags of suitable size and the nucleus card of Trichogramma are introduced in it. The easiest way to accomplish this is to place a piece of ‘Tricho egg card’ containing parasitized eggs (i.e. pharate adults) that are ready to yield the adults and to hold them in subdued light for 2 to 3 days.
- The emerging parasites readily parasitize the fresh eggs. The parasitoid - host ratio is adjusted accordingly to 1:6 get effective parasitism.
- The parasitized eggs in the Tricho Card turn back in 3 or 4 days and the adult parasitoids emerge in 8 to 10 days from the date of parasitization.
- The parasitized eggs in which the parasitoids in the larval or pupal stage (i.e. before or after turning black) can be stored in the refrigerator (at 50C) for about 3 weeks without any loss in emergence.
Precautions
Poor quality of mass reared Trichogramma can result in control failures. The artificial conditions of mass rearing can select for genetic changes that reduce the effectiveness of the Trichogramma in the field. Such rearing conditions include rearing multiple generations on unnatural host eggs, the absence of plants, crowding and interference, rapid generation time, and failure to rejuvenate genetic stock. Except for obvious problems such as lack of adult emergence or wing deformities, growers and pest consultants cannot detect poor quality Trichogramma prior to release. Commercial suppliers are responsible for maintaining desirable characteristics necessary for good performance in the field. Production colonies should be periodically replaced with individuals from a stock culture maintained on the natural or target host. Suppliers also should assess the per cent host egg parasitization, adult emergence, and the sex ratio of emerged adults to be sure they are within acceptable standards. Standards for established cultures on Corcyraare 95±5 per cent egg parasitization, 90±5 per cent adult emergence, and a sex ratio of 1 to 1.5 females per male.
Delivery
Tricho cards are delivered for use in the field. The cards in volumes of 6 cc as per TNAU method of production are assembled in aerated polythene bags and packed in paper cartons for transport. The cards have to be transported by the most rapid method of transport to reach the destination. During transport and holding the cartons should not be exposed to extreme conditions like toxic fumes, open sunlight, high temperature areas as the consignment could be damaged leading to mortality of the Trichogrammastages.
Field release
The parasitoids are released in the pharate stage or when few adults begin to emerge from the host egg during the evening hours. The cards are cut into bits neatly along the grids with least damage to the eggs and stapled beneath the foliage in the upper canopy level. To maximize the field parasitization it is recommended to release the parasitoids is as many locations as possible. Recently scientists are beginning to advocate the release of cards @ 1/5m row length.
|
